I have the Kindle Fire HD and I like it. As any other tablet it is however
mostly useless for reading novels: you'll want the Kindle or another e-ink
device for that.
I'm unsure about this, but maybe the KF has an HDMI output port which the
Nexus 7 doesn't have. That thing is quite useful, if you watch movies and
want to see them on a big TV instead of a small tablet of course.
Cheers,
Michele.